The present invention relates to means for changing the spindle inertia of the spindle of a machining center to provide the proper inertia for heavy cutting or the light cutting, the change being achieved by a transfer means which is provided internally of the apparatus.
Formerly, in a conventional machining center, the operation has been inefficient because the conventional type of machining center has no flywheel and, moreover, it has been operated with the same spindle system inertia not only for heavy cutting such as milling work but also for light cutting such as tapping work.